Self-tapping non-conductive fastener



Jul 25,1961 '8. G. FQRMAN 2,993,950

SELF -TAPPING NON-CONDUCTIVE FASTENER Filed June 17, 1959 BENJAMIN G. FORMAN INVENTOR.

BY ME 7% ATTORNEY United States Patent 2,993,950 SELF-TAPPING NON-CONDUCTIVE FAS'IENER Benjamin G. Fol-man, Queens, N.Y., assignor to Formal- Industries, Inc., Chicago, 11]., a corporation of Illinois Filed June 17, 1959, Ser. No. 820,971

3 Claims. (Cl. 174-138) the casing element at a point where the threaded opening in which the device is engaged is completely formed.

It is among the principal objects of the invention to provide an'improved non-conductive fastener possessed of the above characteristic which may be manufactured by mass production techniques existing in the art, thereby permitting devices embodying the invention to be manufactured at reasonably low cost, with consequent wide sale, distribution and use.

Another object of the invention lies in the provision of an improved index means whereby the correct and rapid assembly of the component parts is facilitated.

improved self tapping non-conductive fastener possessed of the above advantages, which will be so constructed as to be completely insulative with respect to those portions of the same which will be exposed not withstanding the presence of an exposed tapping portion at the leading end of the threaded shank.

A feature of the invention lies in the ready adaptability of the same to such well known molding techniques as injection molding, insert molding and the like.

Another feature of the invention lies in the fact that a wide range of synthetic resinous and metallic materials may be employed in the manufacture of the inventive devices.

These advantages and features, as well as other in cidental ends and advantages will become more clearly apparent during the course of the following disclosure, and be pointed out in the appended claims.

In the drawing, to which reference will be made in the specifications, similar reference characteristics have been employed to designate corresponding parts in the several views.

FIGURE 1 is an exploded view in elevation of an embodiment of the invention.

FIGURE 2 is an end elevational view as seen from the plane 2-2.

FIGURE 3 is an enlarged central longitudinal sectional view partly in elevation.

FIGURE 4 is a transverse sectional view as seen in the plane 4-4 in FIGURE 3.

FIGURE 5 is a transverse sectional view as seen from the plane 5-5 in FIGURE 3.

In accordance with the invention, the device, generally indicated by reference character 10, comprises broadly: a metallic core element 11, a synthetic resinous body or casing element 12, an insulating plug element 13, and a metallic tapping element 14.

The metallic core element 11 is of rectilinear elongated polygonal configuration, and includes a first end 16, a second end 17, and a plurality of planar sides generally indicated by reference character 18 which define a hollow bore 19. In the form illustrated in the drawings, the

.30 A feature of the invention lies in the provision of an bore 19 is of a configuration corresponding to that of a standard recessed head screw, so that the first end 16 may be readily engaged by a conventional driving tool of polygonal cross-section, as for example, the well known Allen-type wrench.

. The casing or body element .12 is preferably formed in situ about the core element 11 by any well known molding technique, as for example, insert molding, and is formed of nylon, or other suitable synthetic resin having similarproperties. It includes a head portion 23 and a threaded integrally formed shank portion 24. The head portion 23 may be of any desired configuration, including a cylindrical outer surface 26, an upper conically shaped. surface 27 and a top surface 28 coextensive with the first end 16 of the core element 11. The threaded shank portion 24 includes an inner surface 30 in intimate contact with the outer surface of the sides 18 of the core element 11 and an outer surface 31 having a continuous thread 32 thereon.

The plug element 13 is adapted to be inserted into the open first end 16 of the core element 11, in order to completely cover the exposed metal surface thereof after shank member 36, the cross-section of which corresponds to that of the end 16, and the dimensions of which are such as to permit frictional retention of the plug ele- .ment 13 within the end 16. As best seen in FIGURES 1 and 3, the shank member 36 is provided with a chamlfered portion 37 to permit. easy insertion.

The'top or cap member 35 includes an upper surface 38 which may be impressed with a suitable decorative design as suggested in FIGURE 2, and a lower surface 39, the area of which is suflicient to completely overlie exposed end 16 of the core element 11.

The metallic tapping element 14 is preferably formed as a small die casting, and includes a polygonal shank member 42 as well as a cutting tip member 43 integrally formed therewith. As is the case with the plug element 13, the free end 45 of the shank member 42 is preferably chamfered to facilitate insertion and engagement with the second end 17 of the core element 11. The cutting tip member 43 includes an abutting surface 47 engage able with the end surface 46 of the threaded shank portion 24. The quasi-conical body portion 48 is provided with cutting thread 49 in such manner that when the element 14 is engaged within the second end 17 of the core element 11, the thread 49 forms a continuation of the thread 32, as best seen in FIGURE 3.

Since the elements 14 and 12 are formed by molding processes in which accuracy may be maintained to reasonably small tolerances, accurate fit is obtained by merely indexing the polygonal shank member 42 with respect to the bore 19 to the position where the end 50 of the thread 49 is aligned with the end 51 of the thread 32. Where the device is assembled by mechanical means, suitable keying means (not shown) may be provided to insure that proper indexing will be obtained during each assembly operation.

In use, the device may be installed within an untapped opening in the normal manner, a tool being engaged with the first end 16 of the core element 11, the metallic cutting thread 49 simultaneously expanding and tapping the hole to full diameter. The tapping operation is completed before the engagement of the threads 32 enters the now tapped hole, so that no damage occurs to the threads 32 which are formed of synthetic resinous material. Upon completion of the tightening of the device 10 within the tapped opening, the driving tool (not shown) is removed to be replaced by the insertion of the shank member 36, following which pressure is applied upon the top or cap member 35 to fully seat the plug element within the opening formed by the first end 16.

In this condition, no metallic parts of the device are exposed to contact, and should the metallic tapping element 14 contact a source of electrical potential, current can be transmitted only through the metallic core element 11, so that it is not transmitted to the edge of the tapped opening, or the head of the device itself.

Should it be desirable to remove the device from contact with the tapped hole, it is necessary only to pry off the plug element 13, and reinsert the tool used for tightening the device, to drive the device in a reverse direction.

It may thus be seen that I have invented novel and highly useful improvements in self-tapping non-conductive fastener devices, in which a metallic tapping element is incorporated into the device in such manner that electrical shorting, or shocking a user of a device in which the fastener is installed is substantially impossible. By resort to injection and insert molding techniques, the cost of manufacture of the devices may be kept at a reasonably low order, and in mass production assembly of large electrical devices, the additional cost involved is more than justified by the elimination of potential shock hazard.

I wish it to be understood that I do not consider the invention limited to the precise details of structure shown and set forth in this specification, for obvious modifications will occur to those skilled in the art to which the invention relates.

I claim:

1. A self-tapping non-conducting fastener, comprising: a metallic hollow core element, an outer body element of synthetic resinous non-conductive material surrounding co-extensively said core element, and having a threaded outer surface thereon, a metallic thread cutting tip engageable with one end of said hollow core element, said tip having a cutting thread thereon forming a continuation of said threaded outer surface of said body element.

2. A self-tapping non-conductive fastener, comprising: a hollow metallic core element having a polygonally shaped cross section, an outer body element of synthetic resinous non-conductive material surrounding co-extensively said core element and having a threaded outer surface thereon, a metallic thread cutting tip having a polygonally shaped shank member thereon engageable within one end of said hollow core element, said tip having a cutting thread thereon forming a continuation of said threaded outer surface of said body element.

ing a cutting thread thereon forming a continuation of said threaded outer surface of said body element; the opposite end of said core element forming tool engaging means, and plug means selectively engageable within said tool engaging means to completely close the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,244,046 Bradshaw June 3, 1941 2,292,102 Cluett Aug. 4, 1942 2,432,986 Forman Dec. 23, 1947 FOREIGN PATENTS 585,887 Great Britain Feb. 27, 1947 

